Aquatic Conservation: Marine and Freshwater Ecosystems

The north coast of mainland Portugal supports a strong dolphin presence and extensive fishing activity, increasing the likelihood of interactions, such as bycatch. This study provides an initial assessment of potential conflict areas, using automatic identification system (AIS) data from Global Fishing Watch. To this end, sighting data from the ATLANTIDA project (2021-2024) on the common dolphin (Delphinus delphis) were used to describe spatiotemporal patterns of occurrence and encounter rates, and to predict their association with fishing effort to identify and map areas of potential overlap. A generalised additive model (GAM) was then applied, integrating environmental, spatial, temporal, and fisheries-related variables to identify the main predictors of species occurrence. Common dolphins were frequently observed during the summer, with an average encounter rate of 3.662 sightings/km. This high encounter rate may be associated with factors such as sea surface temperature, diet, and purse seine fishing activity. The maps showed a spatial overlap between fishing grounds and areas of common dolphin occurrence. Fishing effort was nearly identical between locations with sightings (2.00 h/km{superscript 2}) and those without (1.62 h/km{superscript 2}), suggesting that dolphins are not actively avoiding fishing areas but may instead frequent them due to shared habitat preferences. The best-fitted GAM indicated that encounters were related to year, latitude, fishing effort, depth, sea surface temperature, and season. There was an increase in occurrence over the years and a decrease with increasing fishing effort and sea surface temperature, possibly linked to changes in prey availability, although broad confidence intervals warrant cautious interpretation. Despite some limitations encountered in this study, we believe our findings provide valuable insights into the relationship between dolphin occurrence, environmental conditions, and fishing activities in the area, establishing an important baseline for future conservation and fisheries management efforts.

Vessel-whale collisions are a growing global concern and remain challenging to quantify. Therefore, the use of proxies, such as Close Encounters (CEs) that comprise Surprise Encounters (SEs) and Near-Miss Events (NMEs), has been proposed and widely employed to assess collision risk. To better understand this risk in the Eastern North Atlantic, where maritime traffic is intensive, this study aimed to redefine and quantify CEs, and to assess detectability-related variables that may affect CE identification. CEs were assessed using a cetacean occurrence dataset collected between 2012 and 2024 on board cargo ships and oceanographic vessels. CEs thresholds were redefined based on Time to Potential Collision (TPC), rather than distance alone (as described in literature), to allow a more dynamic, risk-based, and speed-sensitive approach. In total, 1226 sightings of whales (baleen, sperm, and beaked whales) were recorded, of which 37.4% were classified as SEs and 2.0% as NMEs. The sperm whale, Physeter macrocephalus, was the species most frequently involved in CEs (13.9% of all CEs), followed by the Cuviers beaked whale, Ziphius cavirostris (11.8%). A Generalized Additive Model was used to assess the influence of detectability-related variables (i.e., meteorological conditions, whale taxa, vessel characteristics, and Marine Mammals Observers (MMOs) experience) on TPC. Significantly lower TPC values were observed with beaked whales, cargo ships, poor visibility conditions, and less experienced MMOs. The results of this study provide an CEs assessment in this region and contribute to the ongoing efforts to standardize CE quantification, by using TPC as a metric. This work also highlights the importance of decreased speeds and the presence of experienced MMOs on board to increase detection probability and TPC, thereby potentially minimizing collision risk.

Removing river barriers - such as dams or weirs - is an increasingly used strategy for restoring freshwater ecosystems. In Europe, these actions are key for achieving the goal of 25,000 kilometers of free-flowing rivers that the recent regulation on nature restoration establishes for 2030. However, social acceptance remains uneven, and local opposition--often related to cultural attachments, poor ecological awareness, and misinformation--may influence or even impede restoration efforts. Among stakeholders, anglers play a particularly influential role, yet their perceptions and knowledge remain poorly documented. This study addresses how anglers from three river basins in Northern Spain perceive river barriers, their removal, and their ecological impacts, and contrasts their attitudes to those of other residents. We carried out a telephone survey of 1,200 adult residents in the target basins. We assessed perceptions, misconceptions, and self-reported knowledge of river barriers, and collected various sociodemographic parameters. We selected 180 self-identified anglers and compared their answers to those from a subsample of 180 non-anglers with similar demographic characteristics. Despite reporting significantly higher self-perceived knowledge and more polarised responses, anglers showed lower awareness of the ecological impacts of fluvial barriers. They were more likely to underestimate their negative effects compared to the control group. In addition to falling for the main misconceptions surrounding the issue, their responses displayed a degree of bimodality, suggesting that the type of fishing practised may influence their attitudes. Our findings reaffirm the importance of strengthening awareness-raising efforts among relevant stakeholders about the impacts of river barriers and the benefits of their removal when planning specific interventions. It is essential to engage local communities--particularly key groups such as anglers--to strengthen the social acceptance of such actions and improve environmental governance.

We investigate the impact of apex predator absence on the food web structure and ecological balance of freshwater stream ecosystems at the Salto Morato Natural Reserve, Brazil. Despite the absence of fish due to a natural barrier, species richness in upstream pools was not significantly affected, suggesting ecological balance. Detailed food web analysis revealed that the upstream food web has a higher proportion of top predators, predominantly predatory insect larvae, and lower complexity metrics compared to the downstream web. Our findings challenge the traditional concept of mesopredator release and highlight the unique dynamics of predator-less ecosystems, emphasizing the need for tailored conservation strategies for such fragile environments.

Coral restoration is recognised as a critical tool to mitigate pantropical degradation of reef ecosystems. Robust monitoring of restoration progress is crucial for projects to evaluate their success, improve practice, and share knowledge. However, traditional visual surveys often fail to capture the full impact of coral restoration on reef function. Therefore, we employed Passive Acoustic Monitoring (PAM) to assess whether the soundscape of a coral restoration site in the Seychelles differs from adjacent healthy and degraded reference reefs. We applied two methods of soundscape analysis: manual detection of unidentified fish sounds; and machine learning-based Uniform Manifold Approximation and Projection analysis. Results were approach-specific: the manual approach highlighted similarities in fish calls between the restoration site and the healthy reference reef, while the machine learning approach extracted broader soundscape patterns, clustering the restoration site alongside the degraded reference reef. Although this is a single-site study, these findings suggest that a) coral restoration alters reef soundscapes, though recovery time may be taxon-specific, and b) multiple metrics are needed to bridge single-taxon and broad soundscape scales. This study contributes to the evolving field of soundscape ecology in coral reef ecosystems, highlighting the utility of PAM in monitoring changes to reef function through coral restoration.

The shorthead anchovy Encrasicholina heteroloba is a small pelagic species of significant economic and nutritional importance in Tanzania. However, reliable stock assessment remains challenging because of limited data. This study evaluates the status of E. heteroloba in Tanzanias coastal waters and provides management insights for sustainable exploitation. A total of 32,324 specimens were sampled between July 2023 and December 2024. Length-frequency data were cleaned, bootstrapped, and analyzed using the ELEFAN routine to estimate von Bertalanffy growth parameters and mortality rates. Stock biomass and abundance were estimated through virtual population analysis. Estimated parameters were asymptotic length (L{infty}) = 8.42 cm total length, growth coefficient (K) = 2.08, growth performance index ({emptyset}') = 2.19, current fishing mortality (Fcurr) = 0.85, exploitation rate (Ecurr) = 0.40, and length at first capture (Lcurr) = 6.10 cm total length. Natural mortality (M) was 1.25 and total mortality (Z) was 2.10. Overall biomass and stock abundance were 72,725 metric tons and 4.37 x 1010 individuals, respectively. Estimates of biological reference points were F0.1= 1.57, F0.5 = 1.06, and Fmax= 3.34. The results indicate that the stock of E. heteroloba in this region is currently underexploited. Fishing mortality could be moderately increased to enhance yield-per-recruit sustainably.

Simpsonaias ambigua (Salamander Mussel), is a small and thin shelled freshwater mussel often found in difficult to survey habitats, such as beneath slab stones, in the crevices of rock walls, or buried within roots of emergent vegetation and in undercuts of banks. The use of environmental DNA (eDNA - genetic material released from urine, waste, mucus, or sloughed cells) sampling may improve detection and assessment of presence / absence for this rare mussel in comparison to visual tactile techniques. This study completed side by side comparisons of traditional mussel searches and eDNA for a direct assessment of mussel detection efficiencies. Surveying was conducted in several waterbodies of different habitat characteristics with varying abundances of S. ambigua. Additionally, a broad assessment of S. ambigua presence was conducted throughout the proposed critical habitat reach of the Blanchard River in northwest Ohio, to assess if the species remained extant. All eDNA samples were also assessed for the presence of Necturus maculosus (Mudpuppy), the obligate host species for S. ambigua. The eDNA sampling successfully detected S. ambigua from multiple sites and watersheds where it was found with visual surveys. In some cases, eDNA detections occurred in locations where over 16 hours of search yielded only a single individual or fresh dead shells, supporting the sensitivity of eDNA for detection of rare species. Furthermore, probability of detection analysis suggests eDNA sampling can provide high detection efficiency with relatively low effort in comparison to visual searches. The development and validation of an eDNA protocol for the simultaneous detection of S. ambigua and its host salamander increases survey efficiency, reduces field costs, and can support future conservation efforts for listing drainages of extant populations and monitoring conservation goals.

Red Knots (Calidris canutus rufa) rely on Atlantic horseshoe crab (Limulus polyphemus) eggs in the Delaware Bay to refuel during northward migration. Intensive harvest of horseshoe crabs in the 1990s contributed to declines in Red Knot numbers. In 2013, the Atlantic States Marine Fisheries Commission adopted an Adaptive Resource Management (ARM) framework to balance sustainable horseshoe crab harvest with ecosystem integrity and Red Knot recovery, requiring annual stopover population estimates. We estimated the 2025 passage population of Red Knots at Delaware Bay using a Bayesian analysis of a Jolly-Seber mark-resight model which accounts for population turnover and imperfect detection. We also evaluated change in migration timing between 2011 and 2025 with model-derived estimates of arrival at the Delaware Bay each year. The 2025 passage population was 54,043 individuals (95% credible interval: 47,926-61,928), an increase of approximately 17% over 2024 and only the second year since 2011 to exceed 50,000 individuals. Despite the increase, overlapping credible intervals across years indicate a stable stopover population. Migration timing has remained consistent, with 50% of the population typically arriving by 18 May and no evidence of advancement since 2011. These findings provide meaningful input for the ARM framework, supporting sustainable harvest of horseshoe crabs while maintaining adequate foraging opportunities for Red Knots and other shorebirds. Parts of the Introduction, Methods, and Appendices were originally published in Lyons (2024) and are summarized herein.

Since 1995, European fisheries of Pecten maximus have faced the presence of Pseudo-nitzschia species, which are able to produce the neurotoxin domoic acid responsible for Amnesic Shellfish Poisoning (ASP). As filter-feeders, scallops can accumulate and retain domoic acid much longer than most other bivalves, from months to years. When concentrations exceed the regulatory threshold, fisheries are closed leading to economic concern. Inter-individual variability increases the difficulty to predict the depuration dynamics. Quantifying the correlations between domoic acid depuration in P. maximus and individual physiological traits, particularly body size, could improve the understanding of contamination and depuration. We analysed toxin dynamics in organs and assessed the effects of body size and growth. This analysis was based on two datasets from an experimental and an in situ depuration monitoring of P. maximus exposed to a natural bloom of toxic P. australis. Results showed that the distribution of domoic acid shifted among organs between contamination and two months of depuration. Toxin concentrations correlated negatively with body size during contamination and after two months of depuration, but shifted to a positive correlation after 7 months of depuration. This suggested that smaller scallops both accumulate more domoic acid and depurate it more rapidly. Dilution by growth appeared to explain the inversion of the correlation between domoic acid and body size throughout depuration. These results yield useful information for modelling these mechanisms, thus providing valuable tools for scallop fishery management facing ASP. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=60 SRC="FIGDIR/small/708139v1_ufig1.gif" ALT="Figure 1"> View larger version (16K): org.highwire.dtl.DTLVardef@1fd317org.highwire.dtl.DTLVardef@15b9032org.highwire.dtl.DTLVardef@57dae8org.highwire.dtl.DTLVardef@1e4c7fc_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIExperimental and in situ datasets allowed to quantify DA proportion dynamics in organs in P. maximus C_LIO_LIDA concentration and body size are negatively correlated during contamination phase, but positively after a 7-month depuration C_LIO_LIConsidering dilution by growth is important for young scallops to assess DA depuration dynamics C_LIO_LIBoth depuration rate and dilution by growth need to be considered to model DA depuration over the whole scallop size range C_LI

O_LIEnvironmental DNA (eDNA) metabarcoding of water samples is increasingly used to detect fish species in streams. Several studies have concluded that it can outperform traditional inventory methods and recommend using it at large scales for fish-based ecological assessments. However, there is no standard protocol that can guarantee sufficient detection rates and repeatability, despite companies offering an extensive range of analyses. C_LIO_LIWe compared eDNA metabarcoding performed by four companies. Following their guidelines, samples were collected in a small tropical stream in the Maroni River (French Guiana) that hosts a species-rich fish community. We compared their inventories to each other and to a list of species captured during an extensive fish inventory performed immediately after sampling eDNA, as well as to current data on the species distributions. C_LIO_LIThe number of species detected by eDNA metabarcoding ranged from 5 to 48 among the companies, but these inventories contained many inaccuracies. All companies combined, 63 species were detected, of which 10 (16%) had never been reported in the Maroni River. The extensive inventory identified 50 species in the local fish community, of which 16-46 were not detected by eDNA metabarcoding (i.e. false negative detection rate of 32%-92% among the companies). C_LIO_LIReanalysis of raw sequencing data decreased differences among companies greatly, highlighting the importance of using a comprehensive and accurate DNA barcode database to assign species. Dissimilarity indices, calculated to compare the local fish community (based on presence/absence or fish catches) to eDNA detection, revealed large differences regardless of the company. C_LIO_LISummary and applications. The large percentage of species not detected by eDNA metabarcoding of water samples could strongly bias fish-diversity inventories in streams that host species-rich communities. This issue is not well documented in the literature, and we recommend that similar studies in the future focus on other stream contexts. The large differences between commercial eDNA inventories and the local fish community challenge the use of eDNA metabarcoding for fish-based ecological assessments of streams. The variable performance of eDNA companies indicates the need for a standard protocol and access to a comprehensive DNA database before beginning large-scale eDNA programmes. C_LI Highlights- eDNA metabarcoding of water samples is widely used to detect species in streams - Detection performances of 4 private companies were compared to an exhaustive fish inventory - The number of undetected species varies from 32 to 92% depending on the company - Such discrepancies challenge the use of eDNA for fish-based ecological assessments

Spanish clam fisheries have contracted sharply over the past two decades, with repeated closures and declining landings affecting coastal livelihoods. Using local ecological knowledge (LEK), we examine how fishers, fishers guild leaders and regional managers interpret (i) ecological change and (ii) the institutional conditions shaping management outcomes in Spains main clam fisheries, focusing on wedge clam (Donax trunculus), striped venus clam (Chamelea gallina) and smooth clam (Callista chione). We conducted 94 semi-structured interviews (April 2024-August 2025) across the Spanish Mediterranean and the south Atlantic coast (Catalonia, Valencian Community, Balearic Islands, Murcia and Andalusia). Stakeholders characterised declines as a cumulative process driven by interacting stressors: climate variability and extremes, coastal habitat alteration, pollution, episodic disease events and fishing pressure intensified by illegal extraction and informal marketing. Governance assessments were predominantly negative, emphasising fragmented authority across administrative scales, delayed or reactive measures, uneven rules among gears exploiting shared stocks, limited user influence in decision-making, and chronic monitoring and enforcement gaps, especially for shore-based fisheries operating outside port-based control points. Overall, LEK closely aligns with scientific evidence on cumulative stressors, suggesting that persistent declines reflect less a lack of ecological understanding than institutional constraints that hinder timely, legitimate and enforceable responses. Policy priorities include climate-adaptive harvest rules linked to environmental indicators, co-produced monitoring, strengthened traceability and compliance, harmonised rules across gears and management units, and improved cross-sector coordination to reduce conflict and safeguard nearshore habitats. HighlightsO_LIStakeholders across Spain describe clam declines as the outcome of interacting ecological, climatic, and governance stressors rather than as the consequence of isolated drivers. C_LIO_LIPerceived drivers differ regionally: climate- and habitat-related pressures dominate the Mediterranean, while effort, illegal fishing, and market dynamics are more salient in the Gulf of Cadiz. C_LIO_LIMost interviewees view management and governance as ineffective, citing fragmented authority, uneven rules among gears and regions, and weak enforcement. C_LIO_LIInformal practices (off-auction sales and poaching) are repeatedly identified as mechanisms undermining legitimacy, traceability, and effort controls--particularly in nearshore wedge clam fisheries. C_LIO_LIPolicy pathways include harmonising cross-scale rules, strengthening monitoring and compliance, and institutionalising co-management that integrates LEK with science. C_LI

Conservation outcomes in the socio-economically disadvantaged regions are strongly influenced by human behaviour, social norms, and existing governance mechanisms. This study examined stakeholder attitudes, perceptions, values, norms and decision-making processes associated with the conservation of freshwater fishes in two neighbouring states in Eastern India - Jharkhand and Bihar. An approach integrating the Conservation Planning Framework (CPF) with the Theory of Planned Behaviour (TPB) and Social Values (SV) enabled the development of four interlinked themes: "livelihood and economic prioritisation over conservation", "constraints on participation", "values and conservation willingness" and "erosion of social and cultural memories of mahseer", indicative of a process of dual extinction faced by these iconic freshwater fishes. Despite the widespread positive attitudes of the stakeholders towards native fishes and freshwater ecosystems, conservation intentions and actions in both states were found to be negatively influenced by feeble communication, prioritisation of aquaculture, institutional rigidity, inadequate conservation education, limited actual behavioural control (ABC) and subjective norms-driven livelihood pressures. However, the presence of active fishermen cooperative societies and stronger relational values among the local communities makes Jharkhand better equipped to implement participatory governance and stakeholder-involved conservation engagement plans. By strategically linking CPF, TPB, and SV, this study demonstrates how human attitudes, behaviour, social norms, and institutional structures interact to shape freshwater fish conservation outcomes in regions where livelihood needs intersect with conservation priorities, thereby offering actionable insights for managing the native freshwater fish diversity.

Effective monitoring of the critically endangered European eel (Anguilla anguilla) is essential for conservation planning and regulatory decision-making, particularly in heavily fragmented rivers. Environmental DNA (eDNA) methods offer sensitive alternatives to traditional surveys, but there is uncertainty around whether targeted assays or community-wide approaches are better suited to achieve monitoring objectives. We compared eDNA metabarcoding and species-specific quantitative PCR (qPCR) for detecting A. anguilla across 145 pumped catchments in the Fens, East Anglia, England. All sites were sampled once initially, and sites negative for A. anguilla were re-sampled based on metabarcoding results. This allowed comparison of detection rates from a single water sample and site-level retrospective identification of sites where qPCR could have identified A. anguilla in earlier samples. The findings were also set in the context of the wider biodiversity information generated by metabarcoding. From the initial (single) water sample, qPCR detected A. anguilla at seven more sites than metabarcoding (17 versus 10). With repeated sampling, metabarcoding detected A. anguilla at 43 sites, including all but one of the sites where qPCR detected A. anguilla, and ten sites where qPCR did not detect A. anguilla within the same number of samples. Indeed, the additional sampling effort required to detect A. anguilla with metabarcoding at sites also positive with qPCR was small relative to the overall sampling effort. Furthermore, metabarcoding additionally detected 28 non-target fish species alongside fish, amphibian and mammal species of conservation concern. Our results highlight trade-offs between target-species sensitivity and the broader ecological information provided by each method, and support metabarcoding as an effective tool for a holistic conservation approach, with the additional community data outweighing the marginally increased sensitivity of qPCR.

Conservation planning for rare, threatened, and endangered species requires basic information for distribution and abundance. Often this information is lacking due to the nature of traditional survey methods which can be time and labor intensive and thus costly. Environmental DNA (eDNA) metabarcoding offers a promising approach for monitoring freshwater mussel assemblages, a taxonomic group that is both highly imperiled and difficult to survey using traditional methods. We evaluated the performance of eDNA metabarcoding across 30 km of Fish Creek, in Ohio and Indiana, U.S.. We compared results to visual surveys conducted at the same sites. eDNA detected 25 mussel species, including four species not observed alive visually, while visual surveys detected 22 live species. Both methods confirmed the presence of three federally protected species, and eDNA uniquely detected Simpsonaias ambigua, a species rarely encountered in conventional surveys. Incorporating detection repeatability improved congruence between methods: high-repeatability detections strongly aligned with visual presence, whereas moderate and low repeatability detections likely represented reach-scale occupancy. Overall, eDNA metabarcoding offers an efficient and sensitive tool for assessing mussel assemblages and can substantially enhance monitoring programs when integrated with species ecology and hydrological context.

The North American beaver (Castor canadensis) is an ecosystem engineer that strongly influences stream hydrology and ecosystems by constructing dams and canals. Previous research has shown that changes in the extent of beaver ponds and wetlands mapped using aerial photographs can serve as a proxy indicator of shifting regional abundance of beavers. In this study we investigated the use of freely available optical satellite data to measure changes in beaver pond surface water area on the 184 km2 Michipicoten Island in Lake Superior (Ontario, Canada) after a large decline in the beaver population that followed the arrival of grey wolves (Canis lupus). Inter-annual variability in pond extents was measured using sub-pixel mapping methods applied to the 30 m resolution Landsat (1985-2023) and 10 m Sentinel-2 (2016-2023) satellite records. After a > 90% decline in the number of surveyed beaver colonies between 2015-2018, beaver pond surface water area was reduced by 38-42% for ponds < 0.5 ha and by 48% for ponds < 0.1 ha by 2023. While these recent ponding reductions occurred during a period of above average precipitation, two previous smaller reductions were associated with low precipitation, water balance index, and Lake Superior water levels, suggesting that they were caused by drought and not beaver colony declines. While further testing is warranted, our results show that satellite-mapped changes in beaver ponds can provide a cost-effective metric for assessing large-scale population trends in the boreal zone.

We developed an agent-based model (ABM) to assess how area-based controls on fishing methods can reduce fishing mortality and population declines. The model incorporates the behavior and distributions of dolphins and fishing vessels, and realistic displacement of fishing effort when protection is extended. Our case study is New Zealand dolphin - Hectors and Maui dolphins. The model was designed and calibrated using pattern-oriented modeling. Our results show that mortality due to entanglement in fishing gears has been reduced thanks to a gradual increase in dolphin protection. However, current protection is not as effective as previously thought, and scarce populations are negatively affected by Allee effects. Neither national nor international goals for reducing bycatch are met by current dolphin protection. The IUCN has recommended banning gillnet and trawl fisheries in New Zealand waters < 100m deep. For most New Zealand dolphin populations, this would be effective in achieving national and international goals for reducing bycatch. Only two populations would require additional protection. This modelling approach is also suitable for assessing impacts of bycatch and ship strikes for other marine species, making it suitable for informing management decisions in many regions.

Invasive round goby Neogobius melanostomus have advanced eastward through the state of New York and provinces of Ontario and Quebec over the past two decades and are approaching Lake Champlain, one of the largest lakes in North America. This manuscript describes international efforts to monitor round goby populations during 2021-2025 on (a) the southern approach to Lake Champlain via the Hudson River and Champlain Canal, and (b) the northern approach to Lake Champlain via the Saint Lawrence River and Richelieu River. Monitoring utilized environmental DNA (eDNA), backpack electrofishing, beach seining, benthic trawling, and viral hemorrhagic septicemia virus (VHSV) testing. In the Champlain Canal, round goby were captured as far north as the downstream side of the C1 dam (97 kilometers [km] from Lake Champlain) while eDNA detections occurred as far north as the upstream side of the C2 dam (90 km from Lake Champlain). In the Richelieu River, round goby were captured as far south as Saint-Marc-sur-Richelieu (82 km from Lake Champlain) while the southern-most eDNA detections occurred near the Canadian side of the international border (4 km from Lake Champlain). Water temperature influenced habitat usage of round goby in the Champlain Canal, with catch rates in near-shore areas declining at < 10 {degrees}C. All VHSV test results were non-detections at the mouth of the Richelieu River, while one positive and two inconclusive results occurred along the Champlain Canal. Together, these data have informed multiple mitigation measures and have implications for management of aquatic invasive species across North America.

Area and time restrictions are widely used in fisheries management for their simplicity and conservation benefits. Static closures (STCs) often fail to protect migratory fish; therefore, real-time closures (RTCs) are increasingly being adopted. However, RTCs require extensive and rapid data collection and analysis. The vessel monitoring system and daily landing reports provide near real-time data on fishing activities and fish abundance. We conducted a management strategy evaluation of RTCs and STCs in the Gulf of Thailand short mackerel fishery to clarify the efficacy of using RTCs to minimise fishing mortality, while considering their appropriate use with surveillance data for a migratory fish. The results support RTCs as more flexible and requiring a smaller closure area compared with STCs to achieve management objectives. We recommend gathering CPUE data on a monthly basis and using the highest CPUE threshold level to define a closure unit; no unit should be shut down until all units achieve the threshold level. Our results validate the efficacy of the RTC strategy for curtailing fishing mortality of a mobile species and demonstrate the effective use of RTCs to mitigate uncertainty in the migratory patterns of the species in an otherwise unpredictable, fluctuating environment.

Uncontrolled carbon dioxide emissions from human activities contribute to ocean warming and acidification. These alterations in ocean chemistry threaten marine organisms, such as the true giant clam, Tridacna gigas, which is already imperiled due to overharvesting and habitat destruction. To gain an understanding of the physiological and molecular responses of T. gigas and its symbiotic dinoflagellates to ocean warming and acidification, we subjected juvenile individuals to different treatments simulating predicted seawater pH (7.6 and 8.0) and temperature (28{degrees}C, 30{degrees}C, 32{degrees}C and 34{degrees}C) levels for the next century. Juvenile giant clams were able to tolerate sustained exposure to temperatures of up to 32{degrees}C and pH as low as 7.6, while exposure to higher temperature (34{degrees}C), regardless of pH level, resulted in total mortality after a week. However, symbiosis was compromised even in the sublethal treatments, as indicated by the decrease in Symbiodiniaceae density and changes in symbiont gene expression. Symbionts significantly upregulated genes involved in splicing, translation, fatty acid metabolism, and DNA repair, which may constitute an adaptive response, while downregulating genes involved in photosynthesis and transmembrane transport, suggests impaired transfer of photosynthates to the host. These findings demonstrate the vulnerability of the juvenile T. gigas holobiont to heat stress, highlighting the critical importance of continued conservation and management alongside efforts to mitigate global changes in ocean conditions to safeguard this iconic marine bivalve. Summary StatementThis study investigates physiological and molecular responses of Tridacna gigas to seawater warming and acidification, providing insights into the potential future of endangered giant clam populations in a changing ocean.

AimFreshwater species face significant challenges from direct and indirect anthropogenic impacts, leading to a global decline in freshwater biodiversity. Protected areas are a key tool for conservation, but their effectiveness in covering freshwater biodiversity remains uncertain. This study assesses the protection coverage of freshwater macroinvertebrates, vertebrates, and macrophytes in Cuba against the 17% and 30% conservation targets set by the Convention on Biological Diversity. LocationCaribbean biodiversity hotspot, including freshwater ecosystems across the Cuban archipelago. MethodsWe analyzed the distribution of 182 freshwater macroinvertebrates, 26 vertebrates, and 19 macrophyte species using an ensemble of four species distribution modeling techniques: Maxent, Boosted Regression Trees (BRT), Random Forest (RF), and Spatial Stream Network (SSN). We evaluated species overlap with Cubas current protected areas and conducted spatial conservation prioritization exercises that (i) included (lock-in) and (ii) excluded (free-choice) existing protected areas. ResultsOur analysis revealed that 41% (90 species) and 71% (161 species) failed to meet the 17% and 30% conservation targets, respectively. Many of the insufficiently protected species are globally threatened or endemic to the Cuban archipelago, heightening their extinction risk. Conservation planning that includes current protected areas requires significantly larger areas to meet the 30% representation target due to redundancy in existing protections. Conversely, excluding current protected areas achieves conservation goals more efficiently with fewer resources. Both approaches highlight the need to improve connectivity, particularly in upstream regions that are often neglected under the current protected area configuration. Main conclusionsFreshwater biodiversity in Cuba is poorly represented within existing protected areas. Meeting the 30% conservation target would require protecting an additional 30-70% of area, with a focus on headwaters and underrepresented taxa. Expanding Cubas National System of Protected Areas (SNAP) to prioritize fresh-water species, particularly endemics, is essential. A spatial conservation planning approach that integrates both lock-in and free-choice strategies can optimize resource use while enhancing connectivity across key rivers and tributaries.